Hydraulic hoist



July 23, 1935.

E. B. GRUBER .HYDRAULI 0 H01 S '1 Filed Jan. 3, 1953 IN VENTOR.

,MwyM

ATTORNEY Pa tented July 23, less UNITED STATES PATENT OFFICE ammo ' nrnns'uuo nors'r I Earl B. Gruber, Wauwa Hell 00., Milwaukee,

Wisconsin Wis. or to The is., a m nds: of

The present invention relates in general to improvements in the art of lifting and lowering objects with the aid of mechanical power, and

relates more specifically to improvements in they construction and operation of hydraulic hoists such'as are customarily employed to actuate the bodies of dump trucks or the like.

Generally defined, an object of the invention is to provide simple and effective means for improving the action of hydraulic hoists of the general type wherein the elevating member is raised a with the aid of a pump which forces liquid such as oil from a storage reservoir to a space beneath.

the member, while lowering is effected by bypassing the oil from this space around the pump and back to the reservoir.

In the operation of hydraulic hoists of the general type above described, it is customary to provide an automatic valve for permitting liquid to circulate through the pump under high pressure, when the elevating member has reached the upper limit of its stroke, or when the upward .movement of this member has been otherwise checked. If the operation of the pump is continued at such times, the pumping mechanism is subjected to an extreme load because of the fact that the liquid is being circulated therethrough at high pressure sufilcient to maintain the automatic relief valve open. and this pressure is even higher than that required for normal actuation of the elevating member.

It is therefore a more specific object of the present invention to provide improved means for automatically relieving the pumps of systems of the above described general class, from the abnormal duty to which such pumps are subjected at times when the pumps are kept in operation and the hoists are sustaining loads.

Another specific object of the invention is to provide an improved relief valve for a continuously operating liquid pump, which will automatically unload the pump under certain conditions of operation.

A further specific object of the invention is to provide a simple, compact and highly efficient automatic unloading device which is especially applicable to rotary gear pumps for actuating hydraulic hoists or the like.

These and other objects of the invention will be 50 apparent from the following detailed description.

A clear conception of an embodiment of the invention and of the mode of constructing and of operating hydraulic hoists built in accordance therewith, may be had by referring to the draw- 66 mg accompanying and forming a part of this specification in which like reference characters designate the same or similar parts in the various portions of the figure.

The single figure of the drawing is a part sectional side view of a telescopic hydraulic hoist 6 system, showing the hoisting cylinder, the liquid supply reservoir, the circulating pump and the improved automatic relief valve in section.

While the invention will be described herein as being specifically applied to a multiple cylinl0 der quadruple telescopic hoist especially adapted for use on dump trucks, it is not intended to limit the scope by such specific disclosure, and the improved features may obviously be more generally applicable.

Referring to the drawing, the hydraulic hoist system is of relatively standard form and comprises generally, one or more main cylinders I pivotally supported upon the chassis 8 of a vehicle by means of trunnions I; a plurality of telescoping pistons or members 8, 9, i0, ll slidably mounted within each cylinder 5 and pivotally connected to the tilting body II of the vehicle by means of a pivot shaft ii; a rotary gear pump it supported upon the cylinder 8 and drivingly connectedto the propelling motor of the vehicle by means of a drive shaft II; a liquid storage and supply reservoir ll resiliently mounted upon the chassis i and having a common supply and discharge pipe communicable with the pump; and control valve mechanism interposed between the pump I4 and the pipe I I.

It will be understood, by those familiar with telescopic hoists of this general type,. that when the body I! is being elevated or lowered, the telescopic member I slides within the bore of the cylinder I, the member 8 is slidable within the bore of the member I, the member In is slidable within the bore of the member 9 and the inner member H which is directly attached to the pivot 40 shaft I3 is slidable within the bore of the member Ill. The succession of members 8, 9, in, Il may thus be extended to a considerable height or distance from a relatively compact assemblage when in lowermost position, thus enabling extended raising of the body I 2 relative to the vehicle chassis 8. During such raising and lowering operation, the body I! may swing relative to the hoist by virtue of the pivotal connection afforded by the shaft II, and the hoist may also swing relative to the chassis 0 upon the trunnions I, while the members I, 8, I0, I I move rectilineally with respect to thelongitudinal axis of the cylinder I.

The rotary gear pump it which is swingable I5 with the cylinder 5, is also of well known construction comprising a pair of intermeshing-rotary gears i8 one of which is directly connected to the drive shaft l5, these gears when rotating being adapted to withdraw liquid through a suction port l9 and to positively deliver the same past a discharge valve 26 into a discharge port 2|. The pump discharge port 2| communicates directly with the displacement space 22 of the cylinder 5 beneath the hoisting members 6, 9, I6, through a conduit 23 formed in the cylinder 5, and may also be placed into direct communication with the pump suction port H by manipulation of a manually operable rotary valve 24 the actuation of which may be effected from a remote point such as the driver's cab. The pump suction port I9 is normally in open communication with the supply reservoir l6 through the pipe |1, so that when the valve 24 is closed as shown in the drawing and the pump I4 is placed in operation, liquid will be withdrawn from the reservoir l6 and will be forced by the-pump through the port 2| to the space 22 to thereby elevate the members 8, 9, IO, II. If, however, the valve 24 is opened to connect the ports i6, 2|, the pump I4 will merely circulate liquid therethrough, and in case the members 6, 9, l6, II have been previously elevated, the liquid from within the space 22 will be forced back into the reservoir I6 through the conduit 23, port 2|, valve 24, and pipe H. The reservoir I6 is preferably provided with a vent 25 for permitting the liquid to be delivered from and admitted to the storage space.

The improved automatic relief valve mechanism constituting the present improvement, comprises a casing 26 within which the manual control valve 24 may be mounted, a ball relief valve 21 housed within the casing 26, and a ball check valve 26 also housed within the casing. The casing 26 is provided with a through passage 23 having an intermediate orifice 36 therein and normally connecting the pipe H with the pump suction port l9, and is also provided with a passage 3| in open communication with the pump discharge port 2| and having an intermediate port 32 controllable by the relief valve 21. The valve 21 is constantly urged toward closed position relative to the port 32 by means of a compression spring 33 the lower extremity of which coacts with a plunger 34 coacting directly with the ball valve 21, and the upper extremity of which reacts against a cap 35 engaging a screw plug 36 screwed into the casing 26. The compression of the spring 33 may be predetermined so as to require a definite over-pressure within the passage 3| before the valve 21 will open, and this predetermined compression may be varied by inserting shims between the plug 36 and the casing 26. The ball check valve 26 is freely movable with limited clearance, within a bore 31 in the casing 26, and is adapted to coact with the orifice 36 under certain conditions of operation, to cut off communication between the pipe H and the pump suction port IS. The portion of the bore 31 beneath the ball check valve 26 is closed by a stop plug 36 and communicates with the chamber within which the relief valve 21 is confined.

During normal operation of the hoist, the reservoir I6 is supplied with a sufilcient quantity of liquid, preferably oil, the reservoir I6 is in open communication with the pump suction port l9 through the pipe l1 and passage 26, and the valves 21, 28 are positioned as shown in the drawing.

When the truck body I2 is to be elevated, the pump |4 may be placed in operation thereby causing the pump gears i6 to withdraw liquid from the reservoir I6 and to force the same past the discharge valve 26 and through the port 2| and conduit 23, into the displacement chamber or space 22 whereupon the members 6, 6, i6, II will be raised within the cylinder 5 and will thereby elevate the load. If the upward travel of the members 6, 6, i6, II is checked or stopped for any reason such as by reaching the upper limits of their stroke, and the pump |4 continues to operate and to withdraw liquid from the reservoir I6, the pressure within the discharge port 2|, conduit 23 and passage 3| will rise sufliciently to cause the relief valve 21 to open against the predetermined or fixed pressure normally exerted thereon by the spring 33. This opening of the valve 21 will immediately admit liquid under high pressure through the orifice 32 to the portion of the bore 31 beneath the check valve 26, and will cause this check valve to quickly move upwardly into sealing relation with the orifice 36 as shown in dot and dash lines in the drawing. Such movement of the valves 21, 26 will not reduce the pressure within the space 22 below that required to sustain the load, and any liquid subsequently discharged by the pump M will be delivered past these valves 21, 26, and through the pipe H to the receiver. The moment that the check valve 26 seals the orifice 36, however, the pump M will quickly evacuate the suction port l6 and the portion of the passage 26 which remains in open communication with this port, thereby preventing liquid from subsequently reaching the pump from the suction side and efiectively relieving the pump M from heavy duty. When the check valve 26 closes the suction port IS, the pressure in the passage 3| is reduced sufliciently to cause the spring 33 to close the relief valve 21, and this valve remains closed as long as the check valve 26 remains closed. The evacuation of the suction port will hold the check valve 26 in closed position until subsequently released by operation of the valve 24, and the lack of liquid supply to the pump M will obviously maintain the same unloaded as long as the valves 24, 26 remain closed.

When it becomes desirable to lower the hoisting members 6, 6, 6, it is only necessary to manually open the valve 24' so as to establish communication therethrough between the ports 2| and passage 26. As soon as this is done, the liquid entering the passage 26 and suction port l3, forces the check valve 26 away from the orifice 36 and into its lowermost position, thereby permitting the liquid to flow freely into the reservoir l6 through the pipe l1. The pump H at such times, will again be free to receive liquid and to circulate the same through the ports l6, 2| and the valves 26, 24. It is not necessary, however,

to have the pump [4 in operation when the hoisting members are being lowered. Upon closing of the control valve 24, the same cycle of operations will follow, and the valves 21, 26 will again function to automatically unload the pump l4.

5 From the foregoing description it will be apparent that the present improvement provides simple, compact and highly eflicient means for automatically unloading a positive displacement pump especially when utilized in conjunction with a hydraulic hoist. When the supply of liquid to the pump I4 is cut-oil, while the pump is discharging under high pressure, the power consumption immediately drops-or! to a marked degree, and the present invention not only permits this to be done automatically, but also provides means for automatically restoring the unloading mechanism to normal operating condition. The improvement has proven thoroughly successful in commercial operation, and is readily adapted for convenient application to the various types of hydraulic body hoists now on the market, as well as for other uses.

It should be understood that it is not desired to limit the invention to the exact details of construction and to the precise mode of operation herein shown and described, for various modifications within the scope of the claims may occur to persons skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. In combination, a source of liquid supply, a device operable by liquid under pressure, a continuously operable pump adapted to deliver liquid from said source to said device to operate the latter in one direction, a manually operable valve for connecting said device directly to said source to permit operation of said device in the opposite direction, an automatic valve for returning liquid from said pump directly to said source when said device has been operated to the extreme by said pump, and means operable independently of said manually operable valve and upon opening of said automatic valve for cutting-oil. the supply of liquid from said source to said pump, said cut-oif means being returnable to inactive position by the fluid pressure created by said device when said manually operable valve is adjusted to permit operation of said device in said opposite direction.

2. In combination, a source of liquid supply, a device operable by liquid under pressure, a continuously operable pump adapted to deliver liquid from said source to said device to operate the latter in one direction, a manually operable valve for connecting said device directly to said source to permit operation of said device in the opposite direction, a spring pressed automatic valve for returning liquid from said pump directly to said source when said device has been operated tothe extreme by said pump, and a pressure actuated valve operable independently of said manually operable valve and upon opening of said automatic valve for cutting-oil? the supply of liquid from said source to said pump, said pressure actuated valve being returnable to inactive position by the fluid pressure created by said device when said manually operable valve is adjusted to permit operation of said device in said opposite direction.

3. In combination, a source of liquid supply, a hoist operable by liquid from said source, a continuously operable pump adapted to deliver liquid from said source to said hoist to raise the latter, a manually operable valve for connecting said hoist directly to said source to permit lowering of said hoist, an automatic valve for returning liquid from said pump directly to said source when said hoist is fully raised, and means operable independently of said manually operable valve and only upon opening of said automatic valve for interrupting the supply of liquid from said source to said pump, said interrupting means being returnable to inactive position by the fluid pressure created by said hoist during lowering thereof.

4. In combination, a source of liquid supply, a hoist operable by liquid from said source, a continuously operable pump adapted to deliver liquid from said source to said hoist to raise the latter, a manually operable valve for connecting said hoist directly to said source to permit lowering of said hoist, an automatic spring loaded valve for returning liquid from said pump directly to said source when said hoist is fully raised, and a pressure actuated valve operable independently of said manually operable valve and only upon opening of said automatic valve for interrupting the supply of liquid from said source to said pump, said pressure actuated valve being returnable to inactive position by the fluid pressure created by said hoist during lowering thereof.

5. In combination, a source of fluid supply, a hoist operable by fluid from said source, a continuously operable pump adapted to deliver fluid from said source to said hoist to elevate the latter, a control valve for connecting said hoist directly to said source to permit lowering of said hoist, an automatic valve for returning fluid from said pump directly to said source when said hoist is fully elevated, and a fluid pressure actuated valve operable independently of said control valve and only upon opening of said automatic valve for interrupting the supply of fluid from said source to said pump, said pressure actuated valve being returnable to inactive position by the fluid pressure created by said hoist during lowering thereof.

EARL B. GRUBER. 

